In eukaryotic cells, heterochromatin governs diverse cellular processes such as silencing transcription and maintaining genomic integrity. Once formed, heterochromatin must be transmitted to daughter cells during cell division. Inappropriate gain or loss of heterochromatic structure plays a causal role in cancer. Therefore, studies on how heterochromatin is inherited during S phase or epigenetic inheritance will not only increase our understanding of this basic biological process, but also shed light on how this processgoes awry in cancer cells. The yeast S. cerevisiae offers an excellent model systemto study epigenetic inheritance. Yeast heterochromatin is marked by the presence of hypoacetylated histories and four silent information regulator (Sir) proteins. SirSp and Sir4p associate with hypoacetylated histones H3 and H4for establishment and maintenance of yeast silent chromatin. During DNA synthesis, much of the epigenetic information such as modifications on histones as well as Sir proteins is temporarily disrupted. Immediately after DNAsynthesis, the epigenetic information must be reestablished. Chromatin assemblyfactor 1 (CAF-1) is one of the factors involved in inheritance of epigenetic information. However, the molecular mechanisms by whichCAF-1 functions in this process is not clear. Our long-term goal is to understand how chromatin structures are inherited during the S phase of the cell cycle. The objective of this proposal is to study molecular mechanisms whereby CAF-1functions wtih its modulator and effectorproteins to inherit silent chromatin structure in yeast. These studies will address how heterochromatin is inherited in yeast. Moreover, knowledge gained from these studies will also lead to a better understaning of epigenetic inheritance in mammaliancells and cancer caused by malfunction of this process.